/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 */

package java.lang.management;

import javax.management.openmbean.CompositeData;
import sun.management.ManagementFactoryHelper;
import sun.management.ThreadInfoCompositeData;

import static java.lang.Thread.State.*;

/**
 * Thread information. <tt>ThreadInfo</tt> contains the information
 * about a thread including:
 * <h3>General thread information</h3>
 * <ul>
 * <li>Thread ID.</li>
 * <li>Name of the thread.</li>
 * </ul>
 *
 * <h3>Execution information</h3>
 * <ul>
 * <li>Thread state.</li>
 * <li>The object upon which the thread is blocked due to:
 * <ul>
 * <li>waiting to enter a synchronization block/method, or</li>
 * <li>waiting to be notified in a {@link Object#wait Object.wait} method,
 * or</li>
 * <li>parking due to a {@link java.util.concurrent.locks.LockSupport#park
 * LockSupport.park} call.</li>
 * </ul>
 * </li>
 * <li>The ID of the thread that owns the object
 * that the thread is blocked.</li>
 * <li>Stack trace of the thread.</li>
 * <li>List of object monitors locked by the thread.</li>
 * <li>List of <a href="LockInfo.html#OwnableSynchronizer">
 * ownable synchronizers</a> locked by the thread.</li>
 * </ul>
 *
 * <h4><a name="SyncStats">Synchronization Statistics</a></h4>
 * <ul>
 * <li>The number of times that the thread has blocked for
 * synchronization or waited for notification.</li>
 * <li>The accumulated elapsed time that the thread has blocked
 * for synchronization or waited for notification
 * since {@link ThreadMXBean#setThreadContentionMonitoringEnabled
 * thread contention monitoring}
 * was enabled. Some Java virtual machine implementation
 * may not support this.  The
 * {@link ThreadMXBean#isThreadContentionMonitoringSupported()}
 * method can be used to determine if a Java virtual machine
 * supports this.</li>
 * </ul>
 *
 * <p>This thread information class is designed for use in monitoring of
 * the system, not for synchronization control.
 *
 * <h4>MXBean Mapping</h4>
 * <tt>ThreadInfo</tt> is mapped to a {@link CompositeData CompositeData}
 * with attributes as specified in
 * the {@link #from from} method.
 *
 * @author Mandy Chung
 * @see ThreadMXBean#getThreadInfo
 * @see ThreadMXBean#dumpAllThreads
 * @since 1.5
 */

public class ThreadInfo {

  private String threadName;
  private long threadId;
  private long blockedTime;
  private long blockedCount;
  private long waitedTime;
  private long waitedCount;
  private LockInfo lock;
  private String lockName;
  private long lockOwnerId;
  private String lockOwnerName;
  private boolean inNative;
  private boolean suspended;
  private Thread.State threadState;
  private StackTraceElement[] stackTrace;
  private MonitorInfo[] lockedMonitors;
  private LockInfo[] lockedSynchronizers;

  private static MonitorInfo[] EMPTY_MONITORS = new MonitorInfo[0];
  private static LockInfo[] EMPTY_SYNCS = new LockInfo[0];

  /**
   * Constructor of ThreadInfo created by the JVM
   *
   * @param t Thread
   * @param state Thread state
   * @param lockObj Object on which the thread is blocked
   * @param lockOwner the thread holding the lock
   * @param blockedCount Number of times blocked to enter a lock
   * @param blockedTime Approx time blocked to enter a lock
   * @param waitedCount Number of times waited on a lock
   * @param waitedTime Approx time waited on a lock
   * @param stackTrace Thread stack trace
   */
  private ThreadInfo(Thread t, int state, Object lockObj, Thread lockOwner,
      long blockedCount, long blockedTime,
      long waitedCount, long waitedTime,
      StackTraceElement[] stackTrace) {
    initialize(t, state, lockObj, lockOwner,
        blockedCount, blockedTime,
        waitedCount, waitedTime, stackTrace,
        EMPTY_MONITORS, EMPTY_SYNCS);
  }

  /**
   * Constructor of ThreadInfo created by the JVM
   * for {@link ThreadMXBean#getThreadInfo(long[], boolean, boolean)}
   * and {@link ThreadMXBean#dumpAllThreads}
   *
   * @param t Thread
   * @param state Thread state
   * @param lockObj Object on which the thread is blocked
   * @param lockOwner the thread holding the lock
   * @param blockedCount Number of times blocked to enter a lock
   * @param blockedTime Approx time blocked to enter a lock
   * @param waitedCount Number of times waited on a lock
   * @param waitedTime Approx time waited on a lock
   * @param stackTrace Thread stack trace
   * @param monitors List of locked monitors
   * @param stackDepths List of stack depths
   * @param synchronizers List of locked synchronizers
   */
  private ThreadInfo(Thread t, int state, Object lockObj, Thread lockOwner,
      long blockedCount, long blockedTime,
      long waitedCount, long waitedTime,
      StackTraceElement[] stackTrace,
      Object[] monitors,
      int[] stackDepths,
      Object[] synchronizers) {
    int numMonitors = (monitors == null ? 0 : monitors.length);
    MonitorInfo[] lockedMonitors;
    if (numMonitors == 0) {
      lockedMonitors = EMPTY_MONITORS;
    } else {
      lockedMonitors = new MonitorInfo[numMonitors];
      for (int i = 0; i < numMonitors; i++) {
        Object lock = monitors[i];
        String className = lock.getClass().getName();
        int identityHashCode = System.identityHashCode(lock);
        int depth = stackDepths[i];
        StackTraceElement ste = (depth >= 0 ? stackTrace[depth]
            : null);
        lockedMonitors[i] = new MonitorInfo(className,
            identityHashCode,
            depth,
            ste);
      }
    }

    int numSyncs = (synchronizers == null ? 0 : synchronizers.length);
    LockInfo[] lockedSynchronizers;
    if (numSyncs == 0) {
      lockedSynchronizers = EMPTY_SYNCS;
    } else {
      lockedSynchronizers = new LockInfo[numSyncs];
      for (int i = 0; i < numSyncs; i++) {
        Object lock = synchronizers[i];
        String className = lock.getClass().getName();
        int identityHashCode = System.identityHashCode(lock);
        lockedSynchronizers[i] = new LockInfo(className,
            identityHashCode);
      }
    }

    initialize(t, state, lockObj, lockOwner,
        blockedCount, blockedTime,
        waitedCount, waitedTime, stackTrace,
        lockedMonitors, lockedSynchronizers);
  }

  /**
   * Initialize ThreadInfo object
   *
   * @param t Thread
   * @param state Thread state
   * @param lockObj Object on which the thread is blocked
   * @param lockOwner the thread holding the lock
   * @param blockedCount Number of times blocked to enter a lock
   * @param blockedTime Approx time blocked to enter a lock
   * @param waitedCount Number of times waited on a lock
   * @param waitedTime Approx time waited on a lock
   * @param stackTrace Thread stack trace
   * @param lockedMonitors List of locked monitors
   * @param lockedSynchronizers List of locked synchronizers
   */
  private void initialize(Thread t, int state, Object lockObj, Thread lockOwner,
      long blockedCount, long blockedTime,
      long waitedCount, long waitedTime,
      StackTraceElement[] stackTrace,
      MonitorInfo[] lockedMonitors,
      LockInfo[] lockedSynchronizers) {
    this.threadId = t.getId();
    this.threadName = t.getName();
    this.threadState = ManagementFactoryHelper.toThreadState(state);
    this.suspended = ManagementFactoryHelper.isThreadSuspended(state);
    this.inNative = ManagementFactoryHelper.isThreadRunningNative(state);
    this.blockedCount = blockedCount;
    this.blockedTime = blockedTime;
    this.waitedCount = waitedCount;
    this.waitedTime = waitedTime;

    if (lockObj == null) {
      this.lock = null;
      this.lockName = null;
    } else {
      this.lock = new LockInfo(lockObj);
      this.lockName =
          lock.getClassName() + '@' +
              Integer.toHexString(lock.getIdentityHashCode());
    }
    if (lockOwner == null) {
      this.lockOwnerId = -1;
      this.lockOwnerName = null;
    } else {
      this.lockOwnerId = lockOwner.getId();
      this.lockOwnerName = lockOwner.getName();
    }
    if (stackTrace == null) {
      this.stackTrace = NO_STACK_TRACE;
    } else {
      this.stackTrace = stackTrace;
    }
    this.lockedMonitors = lockedMonitors;
    this.lockedSynchronizers = lockedSynchronizers;
  }

  /*
   * Constructs a <tt>ThreadInfo</tt> object from a
   * {@link CompositeData CompositeData}.
   */
  private ThreadInfo(CompositeData cd) {
    ThreadInfoCompositeData ticd = ThreadInfoCompositeData.getInstance(cd);

    threadId = ticd.threadId();
    threadName = ticd.threadName();
    blockedTime = ticd.blockedTime();
    blockedCount = ticd.blockedCount();
    waitedTime = ticd.waitedTime();
    waitedCount = ticd.waitedCount();
    lockName = ticd.lockName();
    lockOwnerId = ticd.lockOwnerId();
    lockOwnerName = ticd.lockOwnerName();
    threadState = ticd.threadState();
    suspended = ticd.suspended();
    inNative = ticd.inNative();
    stackTrace = ticd.stackTrace();

    // 6.0 attributes
    if (ticd.isCurrentVersion()) {
      lock = ticd.lockInfo();
      lockedMonitors = ticd.lockedMonitors();
      lockedSynchronizers = ticd.lockedSynchronizers();
    } else {
      // lockInfo is a new attribute added in 1.6 ThreadInfo
      // If cd is a 5.0 version, construct the LockInfo object
      //  from the lockName value.
      if (lockName != null) {
        String result[] = lockName.split("@");
        if (result.length == 2) {
          int identityHashCode = Integer.parseInt(result[1], 16);
          lock = new LockInfo(result[0], identityHashCode);
        } else {
          assert result.length == 2;
          lock = null;
        }
      } else {
        lock = null;
      }
      lockedMonitors = EMPTY_MONITORS;
      lockedSynchronizers = EMPTY_SYNCS;
    }
  }

  /**
   * Returns the ID of the thread associated with this <tt>ThreadInfo</tt>.
   *
   * @return the ID of the associated thread.
   */
  public long getThreadId() {
    return threadId;
  }

  /**
   * Returns the name of the thread associated with this <tt>ThreadInfo</tt>.
   *
   * @return the name of the associated thread.
   */
  public String getThreadName() {
    return threadName;
  }

  /**
   * Returns the state of the thread associated with this <tt>ThreadInfo</tt>.
   *
   * @return <tt>Thread.State</tt> of the associated thread.
   */
  public Thread.State getThreadState() {
    return threadState;
  }

  /**
   * Returns the approximate accumulated elapsed time (in milliseconds)
   * that the thread associated with this <tt>ThreadInfo</tt>
   * has blocked to enter or reenter a monitor
   * since thread contention monitoring is enabled.
   * I.e. the total accumulated time the thread has been in the
   * {@link java.lang.Thread.State#BLOCKED BLOCKED} state since thread
   * contention monitoring was last enabled.
   * This method returns <tt>-1</tt> if thread contention monitoring
   * is disabled.
   *
   * <p>The Java virtual machine may measure the time with a high
   * resolution timer.  This statistic is reset when
   * the thread contention monitoring is reenabled.
   *
   * @return the approximate accumulated elapsed time in milliseconds that a thread entered the
   * <tt>BLOCKED</tt> state; <tt>-1</tt> if thread contention monitoring is disabled.
   * @throws java.lang.UnsupportedOperationException if the Java virtual machine does not support
   * this operation.
   * @see ThreadMXBean#isThreadContentionMonitoringSupported
   * @see ThreadMXBean#setThreadContentionMonitoringEnabled
   */
  public long getBlockedTime() {
    return blockedTime;
  }

  /**
   * Returns the total number of times that
   * the thread associated with this <tt>ThreadInfo</tt>
   * blocked to enter or reenter a monitor.
   * I.e. the number of times a thread has been in the
   * {@link java.lang.Thread.State#BLOCKED BLOCKED} state.
   *
   * @return the total number of times that the thread entered the <tt>BLOCKED</tt> state.
   */
  public long getBlockedCount() {
    return blockedCount;
  }

  /**
   * Returns the approximate accumulated elapsed time (in milliseconds)
   * that the thread associated with this <tt>ThreadInfo</tt>
   * has waited for notification
   * since thread contention monitoring is enabled.
   * I.e. the total accumulated time the thread has been in the
   * {@link java.lang.Thread.State#WAITING WAITING}
   * or {@link java.lang.Thread.State#TIMED_WAITING TIMED_WAITING} state
   * since thread contention monitoring is enabled.
   * This method returns <tt>-1</tt> if thread contention monitoring
   * is disabled.
   *
   * <p>The Java virtual machine may measure the time with a high
   * resolution timer.  This statistic is reset when
   * the thread contention monitoring is reenabled.
   *
   * @return the approximate accumulated elapsed time in milliseconds that a thread has been in the
   * <tt>WAITING</tt> or <tt>TIMED_WAITING</tt> state; <tt>-1</tt> if thread contention monitoring
   * is disabled.
   * @throws java.lang.UnsupportedOperationException if the Java virtual machine does not support
   * this operation.
   * @see ThreadMXBean#isThreadContentionMonitoringSupported
   * @see ThreadMXBean#setThreadContentionMonitoringEnabled
   */
  public long getWaitedTime() {
    return waitedTime;
  }

  /**
   * Returns the total number of times that
   * the thread associated with this <tt>ThreadInfo</tt>
   * waited for notification.
   * I.e. the number of times that a thread has been
   * in the {@link java.lang.Thread.State#WAITING WAITING}
   * or {@link java.lang.Thread.State#TIMED_WAITING TIMED_WAITING} state.
   *
   * @return the total number of times that the thread was in the <tt>WAITING</tt> or
   * <tt>TIMED_WAITING</tt> state.
   */
  public long getWaitedCount() {
    return waitedCount;
  }

  /**
   * Returns the <tt>LockInfo</tt> of an object for which
   * the thread associated with this <tt>ThreadInfo</tt>
   * is blocked waiting.
   * A thread can be blocked waiting for one of the following:
   * <ul>
   * <li>an object monitor to be acquired for entering or reentering
   * a synchronization block/method.
   * <br>The thread is in the {@link java.lang.Thread.State#BLOCKED BLOCKED}
   * state waiting to enter the <tt>synchronized</tt> statement
   * or method.
   * <p></li>
   * <li>an object monitor to be notified by another thread.
   * <br>The thread is in the {@link java.lang.Thread.State#WAITING WAITING}
   * or {@link java.lang.Thread.State#TIMED_WAITING TIMED_WAITING} state
   * due to a call to the {@link Object#wait Object.wait} method.
   * <p></li>
   * <li>a synchronization object responsible for the thread parking.
   * <br>The thread is in the {@link java.lang.Thread.State#WAITING WAITING}
   * or {@link java.lang.Thread.State#TIMED_WAITING TIMED_WAITING} state
   * due to a call to the
   * {@link java.util.concurrent.locks.LockSupport#park(Object)
   * LockSupport.park} method.  The synchronization object
   * is the object returned from
   * {@link java.util.concurrent.locks.LockSupport#getBlocker
   * LockSupport.getBlocker} method. Typically it is an
   * <a href="LockInfo.html#OwnableSynchronizer"> ownable synchronizer</a>
   * or a {@link java.util.concurrent.locks.Condition Condition}.</li>
   * </ul>
   *
   * <p>This method returns <tt>null</tt> if the thread is not in any of
   * the above conditions.
   *
   * @return <tt>LockInfo</tt> of an object for which the thread is blocked waiting if any;
   * <tt>null</tt> otherwise.
   * @since 1.6
   */
  public LockInfo getLockInfo() {
    return lock;
  }

  /**
   * Returns the {@link LockInfo#toString string representation}
   * of an object for which the thread associated with this
   * <tt>ThreadInfo</tt> is blocked waiting.
   * This method is equivalent to calling:
   * <blockquote>
   * <pre>
   * getLockInfo().toString()
   * </pre></blockquote>
   *
   * <p>This method will return <tt>null</tt> if this thread is not blocked
   * waiting for any object or if the object is not owned by any thread.
   *
   * @return the string representation of the object on which the thread is blocked if any;
   * <tt>null</tt> otherwise.
   * @see #getLockInfo
   */
  public String getLockName() {
    return lockName;
  }

  /**
   * Returns the ID of the thread which owns the object
   * for which the thread associated with this <tt>ThreadInfo</tt>
   * is blocked waiting.
   * This method will return <tt>-1</tt> if this thread is not blocked
   * waiting for any object or if the object is not owned by any thread.
   *
   * @return the thread ID of the owner thread of the object this thread is blocked on; <tt>-1</tt>
   * if this thread is not blocked or if the object is not owned by any thread.
   * @see #getLockInfo
   */
  public long getLockOwnerId() {
    return lockOwnerId;
  }

  /**
   * Returns the name of the thread which owns the object
   * for which the thread associated with this <tt>ThreadInfo</tt>
   * is blocked waiting.
   * This method will return <tt>null</tt> if this thread is not blocked
   * waiting for any object or if the object is not owned by any thread.
   *
   * @return the name of the thread that owns the object this thread is blocked on; <tt>null</tt> if
   * this thread is not blocked or if the object is not owned by any thread.
   * @see #getLockInfo
   */
  public String getLockOwnerName() {
    return lockOwnerName;
  }

  /**
   * Returns the stack trace of the thread
   * associated with this <tt>ThreadInfo</tt>.
   * If no stack trace was requested for this thread info, this method
   * will return a zero-length array.
   * If the returned array is of non-zero length then the first element of
   * the array represents the top of the stack, which is the most recent
   * method invocation in the sequence.  The last element of the array
   * represents the bottom of the stack, which is the least recent method
   * invocation in the sequence.
   *
   * <p>Some Java virtual machines may, under some circumstances, omit one
   * or more stack frames from the stack trace.  In the extreme case,
   * a virtual machine that has no stack trace information concerning
   * the thread associated with this <tt>ThreadInfo</tt>
   * is permitted to return a zero-length array from this method.
   *
   * @return an array of <tt>StackTraceElement</tt> objects of the thread.
   */
  public StackTraceElement[] getStackTrace() {
    return stackTrace;
  }

  /**
   * Tests if the thread associated with this <tt>ThreadInfo</tt>
   * is suspended.  This method returns <tt>true</tt> if
   * {@link Thread#suspend} has been called.
   *
   * @return <tt>true</tt> if the thread is suspended; <tt>false</tt> otherwise.
   */
  public boolean isSuspended() {
    return suspended;
  }

  /**
   * Tests if the thread associated with this <tt>ThreadInfo</tt>
   * is executing native code via the Java Native Interface (JNI).
   * The JNI native code does not include
   * the virtual machine support code or the compiled native
   * code generated by the virtual machine.
   *
   * @return <tt>true</tt> if the thread is executing native code; <tt>false</tt> otherwise.
   */
  public boolean isInNative() {
    return inNative;
  }

  /**
   * Returns a string representation of this thread info.
   * The format of this string depends on the implementation.
   * The returned string will typically include
   * the {@linkplain #getThreadName thread name},
   * the {@linkplain #getThreadId thread ID},
   * its {@linkplain #getThreadState state},
   * and a {@linkplain #getStackTrace stack trace} if any.
   *
   * @return a string representation of this thread info.
   */
  public String toString() {
    StringBuilder sb = new StringBuilder("\"" + getThreadName() + "\"" +
        " Id=" + getThreadId() + " " +
        getThreadState());
    if (getLockName() != null) {
      sb.append(" on " + getLockName());
    }
    if (getLockOwnerName() != null) {
      sb.append(" owned by \"" + getLockOwnerName() +
          "\" Id=" + getLockOwnerId());
    }
    if (isSuspended()) {
      sb.append(" (suspended)");
    }
    if (isInNative()) {
      sb.append(" (in native)");
    }
    sb.append('\n');
    int i = 0;
    for (; i < stackTrace.length && i < MAX_FRAMES; i++) {
      StackTraceElement ste = stackTrace[i];
      sb.append("\tat " + ste.toString());
      sb.append('\n');
      if (i == 0 && getLockInfo() != null) {
        Thread.State ts = getThreadState();
        switch (ts) {
          case BLOCKED:
            sb.append("\t-  blocked on " + getLockInfo());
            sb.append('\n');
            break;
          case WAITING:
            sb.append("\t-  waiting on " + getLockInfo());
            sb.append('\n');
            break;
          case TIMED_WAITING:
            sb.append("\t-  waiting on " + getLockInfo());
            sb.append('\n');
            break;
          default:
        }
      }

      for (MonitorInfo mi : lockedMonitors) {
        if (mi.getLockedStackDepth() == i) {
          sb.append("\t-  locked " + mi);
          sb.append('\n');
        }
      }
    }
    if (i < stackTrace.length) {
      sb.append("\t...");
      sb.append('\n');
    }

    LockInfo[] locks = getLockedSynchronizers();
    if (locks.length > 0) {
      sb.append("\n\tNumber of locked synchronizers = " + locks.length);
      sb.append('\n');
      for (LockInfo li : locks) {
        sb.append("\t- " + li);
        sb.append('\n');
      }
    }
    sb.append('\n');
    return sb.toString();
  }

  private static final int MAX_FRAMES = 8;

  /**
   * Returns a <tt>ThreadInfo</tt> object represented by the given <tt>CompositeData</tt>. The given
   * <tt>CompositeData</tt> must contain the following attributes unless otherwise specified below:
   * <blockquote> <table border summary="The attributes and their types the given CompositeData
   * contains"> <tr> <th align=left>Attribute Name</th> <th align=left>Type</th> </tr> <tr>
   * <td>threadId</td> <td><tt>java.lang.Long</tt></td> </tr> <tr> <td>threadName</td>
   * <td><tt>java.lang.String</tt></td> </tr> <tr> <td>threadState</td>
   * <td><tt>java.lang.String</tt></td> </tr> <tr> <td>suspended</td>
   * <td><tt>java.lang.Boolean</tt></td> </tr> <tr> <td>inNative</td>
   * <td><tt>java.lang.Boolean</tt></td> </tr> <tr> <td>blockedCount</td>
   * <td><tt>java.lang.Long</tt></td> </tr> <tr> <td>blockedTime</td>
   * <td><tt>java.lang.Long</tt></td> </tr> <tr> <td>waitedCount</td>
   * <td><tt>java.lang.Long</tt></td> </tr> <tr> <td>waitedTime</td> <td><tt>java.lang.Long</tt></td>
   * </tr> <tr> <td>lockInfo</td> <td><tt>javax.management.openmbean.CompositeData</tt> - the mapped
   * type for {@link LockInfo} as specified in the {@link LockInfo#from} method. <p> If <tt>cd</tt>
   * does not contain this attribute, the <tt>LockInfo</tt> object will be constructed from the
   * value of the <tt>lockName</tt> attribute. </td> </tr> <tr> <td>lockName</td>
   * <td><tt>java.lang.String</tt></td> </tr> <tr> <td>lockOwnerId</td>
   * <td><tt>java.lang.Long</tt></td> </tr> <tr> <td>lockOwnerName</td>
   * <td><tt>java.lang.String</tt></td> </tr> <tr> <td><a name="StackTrace">stackTrace</a></td>
   * <td><tt>javax.management.openmbean.CompositeData[]</tt> <p> Each element is a
   * <tt>CompositeData</tt> representing StackTraceElement containing the following attributes:
   * <blockquote> <table cellspacing=1 cellpadding=0 summary="The attributes and their types the
   * given CompositeData contains"> <tr> <th align=left>Attribute Name</th> <th align=left>Type</th>
   * </tr> <tr> <td>className</td> <td><tt>java.lang.String</tt></td> </tr> <tr> <td>methodName</td>
   * <td><tt>java.lang.String</tt></td> </tr> <tr> <td>fileName</td> <td><tt>java.lang.String</tt></td>
   * </tr> <tr> <td>lineNumber</td> <td><tt>java.lang.Integer</tt></td> </tr> <tr>
   * <td>nativeMethod</td> <td><tt>java.lang.Boolean</tt></td> </tr> </table> </blockquote> </td>
   * </tr> <tr> <td>lockedMonitors</td> <td><tt>javax.management.openmbean.CompositeData[]</tt>
   * whose element type is the mapped type for {@link MonitorInfo} as specified in the {@link
   * MonitorInfo#from Monitor.from} method. <p> If <tt>cd</tt> does not contain this attribute, this
   * attribute will be set to an empty array. </td> </tr> <tr> <td>lockedSynchronizers</td>
   * <td><tt>javax.management.openmbean.CompositeData[]</tt> whose element type is the mapped type
   * for {@link LockInfo} as specified in the {@link LockInfo#from} method. <p> If <tt>cd</tt> does
   * not contain this attribute, this attribute will be set to an empty array. </td> </tr> </table>
   * </blockquote>
   *
   * @param cd <tt>CompositeData</tt> representing a <tt>ThreadInfo</tt>
   * @return a <tt>ThreadInfo</tt> object represented by <tt>cd</tt> if <tt>cd</tt> is not
   * <tt>null</tt>; <tt>null</tt> otherwise.
   * @throws IllegalArgumentException if <tt>cd</tt> does not represent a <tt>ThreadInfo</tt> with
   * the attributes described above.
   */
  public static ThreadInfo from(CompositeData cd) {
    if (cd == null) {
      return null;
    }

    if (cd instanceof ThreadInfoCompositeData) {
      return ((ThreadInfoCompositeData) cd).getThreadInfo();
    } else {
      return new ThreadInfo(cd);
    }
  }

  /**
   * Returns an array of {@link MonitorInfo} objects, each of which
   * represents an object monitor currently locked by the thread
   * associated with this <tt>ThreadInfo</tt>.
   * If no locked monitor was requested for this thread info or
   * no monitor is locked by the thread, this method
   * will return a zero-length array.
   *
   * @return an array of <tt>MonitorInfo</tt> objects representing the object monitors locked by the
   * thread.
   * @since 1.6
   */
  public MonitorInfo[] getLockedMonitors() {
    return lockedMonitors;
  }

  /**
   * Returns an array of {@link LockInfo} objects, each of which
   * represents an <a href="LockInfo.html#OwnableSynchronizer">ownable
   * synchronizer</a> currently locked by the thread associated with
   * this <tt>ThreadInfo</tt>.  If no locked synchronizer was
   * requested for this thread info or no synchronizer is locked by
   * the thread, this method will return a zero-length array.
   *
   * @return an array of <tt>LockInfo</tt> objects representing the ownable synchronizers locked by
   * the thread.
   * @since 1.6
   */
  public LockInfo[] getLockedSynchronizers() {
    return lockedSynchronizers;
  }

  private static final StackTraceElement[] NO_STACK_TRACE =
      new StackTraceElement[0];
}
